This invention relates in general to the field of electronics packaging, and in particular to microwave circuitry packaging to meet stringent microwave signal isolation requirements.
Microstrip circuit boards are typically used to provide signal paths at microwave frequencies. Enclosures with no gaps or very small gaps are required to provide isolation between microwave signals in nearby portions of microwave circuits. The smaller the gap size in the microwave circuit enclosure, the higher the microwave signal isolation. Low frequencies, on the order of 100 MegaHertz (MHz), are relatively easy to isolate. High frequency microwave signals for which a high isolation packaging technology is especially desirable can be on the order of 10-20 GigaHertz (GHz).
A traditional approach to provide the necessary microwave signal isolation microwave circuitry is to end mill isolated channels into a relatively thick metallic plate as a base, and then to install microwave components, microstrip circuitry, and the associated electrical interconnections in the desired circuit configuration before fitting a cover onto the package. This approach totally encloses the microstrip circuitry in each covered channel, but leaves wall edges of the milled channels which typically need to be fitted with gaskets to fill gaps where the channels meet the cover of the enclosure. This covered channel approach has several shortcomings, including:
a) separate microstrip segments need to be individually trimmed, positioned, and bonded, which is labor-intensive, and, therefore, an expensive, time-consuming process;
b) quality of the installation is hard to ensure based on the poor access to many areas within the channels, yet the individual trimming, positioning, and bonding provide a high possibility of error; a significant amount of rework can be required for the traditional microstrip enclosures.
c) gaskets for the wall edges take a significant amount of time to install, and can be pinched during assembly of the microstrip enclosure; a pinched gasket can leave a gap in the enclosure and fail to provide isolation for the adjacent microstrip circuitry;
d) milled channels provide poor access to many areas within the channels for assembly operations including wirebonding, soldering, and parallel-gap welding; the installation of components and assembly of the package is thereby slowed, increasing costs;
Thus, what is needed is a method for providing high isolation of microwave signals on microstrip circuitry while decreasing assembly time and difficulty, and increasing microwave signal isolation in a low-cost package.